What will happen is that the metal will stretch flat on the outer radius and you will end up with a necked down diameter. Your best bet is to fill it with sand. But the sand has to be absolutely dry. I've put some aluminum foil on a baking sheet and baked it to make sure it's completely moisture free. Weld a cap on one end of the pipe, fill it with sand stopping about 6" from the top. While your filling, tap on the side of the pipe to pack down the sand. Crumple up some newspaper and insert it in the pipe on top of the sand. Pack down the newspaper. Now you can insert a broom handle in the pipe, though I use an old jack handle from a cheapie craftsman jack I threw away a long time ago. Now, you will absolutely need a rosebud tip. The amount of heat needed is insane. Get a friend to heat up the pipe with the rosebud while you apply pressure to the handle in the direction you want the pipe to bend. You have to get it red hot before it will move. Only apply heat to the outside of the bend and to the sides; the part of the pipe that is in tension. If you heat the inner part of the bend or any part that is in compression, the pipe will buckle and crumple.
You need the right tools or you will just waste your time. A plumber's torch wont do it. You need an oxy-acetylene torch with decent sized tanks. The rosebud uses a lot of fuel. It's hot, time consuming work though. If you plan on making several bends, you'll save time, effort, and money by getting a tubing bender.
Al